A device for extruding a strip of rubber is already known in the state of the art, which device comprises rubber feeder means, e.g. provided with a screw extruder, together with a passage for forming the strip of rubber.
The forming passage is defined firstly by a rotary roller for forming and driving the strip, and secondly by a forming member that is distinct from the roller, and that is placed in register with the roller, e.g. a blade.
In order to form the strip of rubber, the rotating roller acts through the forming passage to entrain the rubber that has been put under pressure by the feeder means.
When the rubber passes through the forming passage, the roller tends to exert surface stresses on a first face of the strip that are different from the stresses exerted by the blade on the second face of the strip. This difference in surface stresses is eliminated by the effect of the traction that is generally exerted on the strip downstream from the forming passage.
When the strip presents a desired length, extrusion is stopped and the extruded strip is cut away at the outlet from the forming passage. When the device restarts, during a transient stage, the rubber front is not subjected to any traction downstream from the forming passage, such that the first and second faces of the extruded strip present a surface tension difference that is not zero.
This tension difference tends to cause the strip to roll up downstream from the forming passage.
Parameters concerning the rubber, such as the adhesion of rubber on the roller, and the composition of the rubber can indeed be modified to limit this rolling-up effect. Nevertheless, those parameters are relatively difficult to control.